Dr Jacqueline Rowarth on our misunderstandings about the role of nitrogen.
The trouble with all this averaging and aggregating up is that farmers may think they need a urea coating when their farm conditions would actually make it unnecessary.
Basically, there is more than one way to skin the N-loss cat.
With the current state of dairy payouts, everyone wants the same thing: the amount of N you get to keep for your plants relative to your conditions in your part of the country.
Under all except the most extreme conditions, e.g. hot, dry and windy and applying high rates of N, the losses in pastoral farming are expected to average 10-15% (or less) of the N applied as urea. Any claim of coated products reducing N loss by, say, 50% can be misleading because that does not mean half of the total applied nitrogen. Rather, the claims mean half of the 10-15% which of course equals 5-7.5%.
How much N does this mean is being saved for plant growth? If you apply 65kg urea/ha (30kg N/ha) and lose 10% to volatilisation, you are losing 3kg N/ha and with the urea coating you will reduce this to 1.5kg N/ha (at 50% reduction of volatilisation).
At times, the premium for a coated product can be 8-10% more than standard urea.
As a famous psychologist once said: “When the only tool you have is a hammer, every problem looks like a nail.” If a fertiliser company with a urea coating tells you it’s the only solution to volatilisation, they should also inform you of the several other ways volatilisation can be tackled.
There are at least five other simple steps you could consider to help reduce volatilisation:
Apply lower rates each application e.g. 30-50kg N/ha (volatilisation rates increase with higher rates of N application)
Apply when it’s raining or about to rain or use at least 10mm of irrigation straight after application
Apply to pastures with some leaf cover
Avoid hot, dry and windy conditions
If applying to soil, incorporate so it is just below the surface.
• Ants Roberts is chief scientific officer at Ravensdown.